1. Field of the Invention
This invention relates to physical quantity sensors that detect physical quantities such as accelerations, vibrations, and inclinations in a two-dimensional manner or in a three-dimensional manner, and relates in particular to electrostatic capacity type piezoelectric sensors that can be manufactured in accordance with semiconductor manufacturing processes.
This application claims priority on Japanese Patent Application No. 2004-31620, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, various types of piezoelectric sensors having abilities of detecting accelerations in a three-dimensional manner have been developed, wherein Japanese Patent Application Publication No. S62-174978 discloses an example of a piezoelectric sensor as shown in FIG. 14.
In the piezoelectric sensor shown in FIG. 14, an X-axis detector 2X, a Y-axis detector 3Y, and a Z-axis detector 4Z are arranged on the main surface of a substrate 1, on which a peripheral circuit 5 is also arranged to process directional information produced by the detectors 2X, 3Y, and 4Z. Herein, both of the X-axis direction and Y-axis direction lie in parallel with the main surface of the substrate 1 having a rectangular shape defined by short sides and long sides, wherein the X-axis direction lies in parallel with the short side of the substrate 1, and the Y-axis direction lies in parallel with the long side of the substrate 1. The Z-axis direction lies vertically perpendicular to the main surface of the substrate 1, and it also lies perpendicular to the X-axis direction and the Y-axis direction respectively.
The X-axis detector has three movable members 2a to 2c, each of which is supported in a cantilever manner and which differ from each other in length, wherein the tip ends of the movable members 2a to 2c are each broadened in width in order to realize weight functions therefor. The movable members 2a to 2c are each subjected to displacement in response to acceleration applied thereto in the X-axis direction, wherein the longer one is increased in displacement. The Y-axis detector 3Y has three movable members 3a to 3c, each of which is supported in a cantilever manner and which differ from each other in length, wherein the tip ends of the movable members 3a to 3c are each broadened in width in order to realize weight functions therefor. The movable members 3a to 3c are each subjected to displacement in response to acceleration applied thereto in the Y-axis direction, wherein the longer one is increased in displacement. Similarly, the Z-axis detector 4Z has three movable members 4a to 4c, each of which is supported in a cantilever manner and which differ from each other in length, wherein the tip ends of the movable members 4a to 4c are each broadened in width in order to realize weight functions therefor. The movable members 4a to 4c are each subjected to displacement in response to acceleration applied thereto in the Z-axis direction, wherein the longer one is increased in displacement.
All of the movable members 2a–2c, 3a–3c, and 4a–4c are produced by etching silicon materials used for the substrate 1, wherein the base portion of each movable member has piezoresistance realized by diffusion resistance. Hence, each movable member can convert displacement thereof into an electric signal by use of the piezoresistance.
As described above, the conventionally known piezoelectric sensor is designed such that the X-axis detector 2X having the movable members 2a–2c, which are specifically used for the detection of the acceleration in the X-axis direction, the Y-axis detector 3Y having the movable members 3a–3c, which are specifically used for the detection of the acceleration in the Y-axis direction, and the Z-axis detector 4Z having the movable members 4a–4c, which are specifically used for the detection of the acceleration in the Z-axis direction, are arranged on the main surface of the substrate 1. This increases the total area occupied by the detectors 2X, 3Y, and 4Z, which in turn increase the overall chip size.